1. Field of the Invention
This invention relates to a camera capable of changing one focal length of the taking lens thereof into another and, particularly, to a variable focus type camera employing a programmed shutter capable of changing an open aperture value of the taking lens into another when a focal length of the camera is changed into another. More particularly, this invention relates to an exposure controlling means and an electronic flash controlling means each for the variable focus type camera so improved as to make a proper exposure and flash timing with a substantially less storage of memories.
Generally, a variable focus type camera is so constructed that the lens system thereof is moved or an auxiliary lens system is attached or detached with moving the main lens system, so that a focal length f of a taking lens may be changed. On the other hand, as is publicly known, in a lens of which principal point coincides with the position of the exit pupil thereof, the following relation can be held good; EQU D/f=1/F
wherein D represents the diameter of an exit pupil, f represents a focal length of a taking lens, and F represents an F number.
Generally in a variable focus type camera having a built-in aperture unit, the abovementioned relation teaches that there is a difference in F number between a short focus lens f(W) and a long focus lens f(T), even if their aperture diameters are the same. In other words, an exposure amount applied onto a film surface when using a f(W) is different from that when using a f(T), even if the shutter speed conditions are the same. FIG. 6 illustrates the above description, wherein it is indicated that the exposure amounts applied onto film surfaces are different from each other when the exposures are made through an electromagnetic programmed shutter under the same shutter speed conditions, i.e., the same exposure time conditions, because F numbers are different from each other when making exposures.
In a camera having a conventional type variable focal lens, an aperture mechanism or the like has been provided to the front of the AE photoreceptor of the camera so as to be changed the aperture values or switched over a filter density, in accordance with the aperture values of the taking lens which are varied according to the changes of the focal length of the taking lens aperture values of a taking lens when the focal length of the lens is changed, and exposures have been compensated. This has made such cameras complicated to construct. On the other hand, in a variable focus type camera using a programmed shutter which makes automatic exposures in accordance with the memory of the shutter speeds corresponding to subject brightness, it has been required to make an automatic exposures in such a manner that the individual tables corresponding to the focal lengths of f(W), f(T) or the other are memorized and the table corresponding to a focal length is called up.
In a camera having an aperture-shutter combination, an exposure amount for electronic flash photography may be controlled by variously changing such an aperture size as indicated by the aperture size variation curve in such a process of opening a shutter as indicated by A in FIG. 6. This has also been publicly known.
In the case that an exposure amount for electronic flash photography is controlled by the moment of starting a flash emission, as mentioned above, it may be considered to take the same means as mentioned above when using a variable focus type camera.
However, in a variable focus type camera, it is necessary to prepare a time table of starting each electronic flash emission for every focal length, so that a large number of memories should be stored.